General performance tip about possibly using the GC or not

[rikki cattermole via Digitalmars-d-learn]

D's GC is stop the world (aka all threads) and does not run on its own 
(requires being asked to collect).

It is only given the opportunity to collect when you allocate (new/more) 
memory. It can decide not to, or to do so at any point making it very 
unpredictable.

This is why we keep saying that it is not a magic bullet.
It isn't. It just does a simple set of logic and nothing more.